Filter unit and method of making the same



Aug. 21, 1945. P, F, MCDERMOTT 2,383,066

FILTER UNIT AND METHOD OF MAKING THE SAME Filed March 25, 1943 @Wa/@LATTORNEY j Patented Aug. 21, 1945 FILTER UNIT AND METHOD F MAKING THESAME Paul F. McDermott, Martinsville, N. J., assignor to Johns-Manvllle, Corporation, New York, N. Y.. a corporation of New YorkApplication March 25, 1943, Serial No. 480.431

(Ui. 18S-44) Claims.

The present invention relates to-filters for the removal of solid orliquid particulate matter such as dust. dirt, smoke, tars. oils, etc..from air and other gases. Filter units in accordance with the inventionare adapted for industrial uses, air conditioning apparatus, respiratorsand the like, the invention not being restricted to any particularapplication. y

The principal object of the invention is the provision of a filter and amethod of making the same, the filter including a continuous interfeltedlayer of fibrous material closely .overlying and supported by aforaminous member or form and of character to secure substantiallycomplete removal of gas-borne particulate materials for relatively longperiods.

More particularly an object of the invention is the provision of afilter unit having low flow resistance and composed. at least for themost part, of` interfelted inorganic fibers such as mineral wool fibers,with a relatively small proportion of a binding material disseminatedthroughout the` felt.

Another object of the invention is the provision of a filter unit inwhich the fibrous filtering layer overlying the foraminous supportingmember is felted in situ. to closely conform with and follow the surfacecontoursv of the supporting member and to provide a continuousuninterrupted layer. The filtering layer may be applied to supportingmembers of cup shape or of any desired configuration.

A still further object of the invention is the provision of a filteringunit or element and a method of making the same. whereby fibers and asuitable binder are deposited directly from a liquid dispersion thereofonto the surface of a matrix comprising the supporting member. As statedabove, preferably the iibers comprise mineral wool fibers, by which termis meant fibers formed of rock, slag, glass, and other similarmaterials. However, the mineral wool fibers may be interpersed, ifdesired, with organic or other fibers.

A still further object ofthe invention is the provision of a method ofwet felting fibrous materials directly onto the surface of a foraminousmatrix, in which the fibers assume positions generally parallel to theface of the matrix.

My invention will 'be more fully understood and further objects andadvantages thereof will become apparent when reference is made to themore detailed description thereof which is to follow and to theaccompanying drawing, in which;

Fig. i is a perspective view. with parts broken away for clearncss ofillustration, depicting a tubular filtering element in accordance withthe invention;

Fig. 2 is a diagrammatic view illustrating a method of making theelement of Fig. 1:

Fig. 3 is a perspective view similar to Fig. 1 of a modified form ofnlter unit:

Fig. 4 is a perspective view similar to Fig. l, of a further form of theinvention; and

Fig. 5 is a detallsectional view on an enlarged scale illustrating amodification oi the invention which may be employed with any of theconstructions of Figs. l, 3 and 4.

Referring now particularly to Fig. i, there is shown a filter unit lcomprising a cylindrical hollow body member if including end members Iland It and a foraminous wall it. One of the end members, for example,end member Il, includes a nipple 2B, secured thereto and communicatinswith the interior of the hollow body l2. End members Il and IB may beformed of any suitable substantially gas-impervious matcrial such assheet metal, wood, plastic or the like. The material forming theforaminous wall Il may be a relatively fine mesh screen or perforatedsheet of metal, plastic or other suitable material providing sumcientrigidity to support the filtering Vlayer during its formation and toretain the shape of the body under service conditions. The end membersmay be crimped, soldered or otherwise secured to the foraminous wall.

Overlying wall Il is a filtering layer or mat 22 comprising interfeltedfibers with a binder in limited quantities dispersed throughout thefelt. The filtering layer is of substantially unlform density andthickness throughout the foraminous wall area of the body completelycovering and closely conforming to the surface contours of the same. Thefibrous layer is interlocked to the foraminous material, at least tosome extent, by penetration of the fibers through the numerous openings.It desired, foraminous material may be used in place of one or both ofthe imperforate end members, in which event the fibrous filtering layeris extended to cover these areas.

Referring now to Fig. 2. the method of forming the ltering layer will bedescribed. The interior of body i2 is connected through nipple 20 to anysuitable source of suction. I'he body is supported by suitable means ina vat 2l containing a furnish comprising a liquid dispersion of fibers2t and of binder 2l. the latter in finely divided form. For the purposesof example. and without limiting the invention, it may be stated that asuitable furnish for this purpose comprises 0.11 part of fibers and0.004 part of binder, well dispersed in 60 parts of water, allproportions by weight.

When the body is immersed in the furnish. the suction line Il is openedto cause flow of liquid through the foraminous wall which serves u amatrix against which the bers are deposited in interfelted relationshipwith the binder particles dispersed throughout -the felted layer. Theinitially deposited fibers lie closely adjacent the foraminous wall and.in many instances, ends of the fibers penetrate the openings to, ineffect, interlock the felted layer to the wall. The felting action iscontinued, with such continuous or intermittent replenishment of thefurnish as may be necessary, until the felted layer is built up to thedesired thickness.

Although the use of suction to cause flow of the furnish to the matrixhas been described, other means may be employed for providing a pressuredifferential across the matrix. For example, pressure may be applied tothe furnish and line 34 be opened to the atmosphere.

To promote uniformity of the fibrous felt or mat over the matrix andalso to obtain a preferred fiber arrangement in which the fibers liesubstantially parallel to the face of the matrix, relative motion may beproduced between the furnish and the matrix. This may be accomplished,as illustrated in Fig. 2, by rotating the matrix slowly in the vat 24 bymeans of a drive 30 connected to any motive source. In this case arotary seal 32 is provided between the stationary vacuum line 34 and a.relatively rotatable section carrying a drive pulley 3| and connected tonipple 20. On the other hand, the vat may be rotated if desired and thematrix and vacuum line held stationary. Similar .eli'ects may beobtained by reciprocating motion of the matrix in the vat. Relativerotary motion will tend to lay the fibers parallel to the face of thematrix and extending circumferentially thereof. Reciprocating movementwill tend to lay the fibers generally parallel to the face of the matrixbut extending axially thereof. Combinations of the above or othermovements of the matrix or vat may be employed to obtain any desiredarrangement of the bers.

When the fibrous mat is built up on the matrix to the desired thickness,the matrix is removed from the furnish and preferably the withdrawal ofair continued for a short time to remove excess moisture from the mat.The completed nlter unit is then placed in an oven and thoroughly dried.

The wet felting of the fibrous layer directly upon the matrix, thelatter constituting the supporting body of the filtering element, coversall or practically all of the fcraminous area with a substantiallyuniform layer oi the felted filtering mat. In some instances it has beendetermined that minor voids are formed particularly adjacent the endcaps of the hollow body. These may readily be sealed to prevent leakageby the use of any suitable or conventional sealing material, forexample, ethyl acetate, latex, asphaltic materials and the like, suchmaterials having the further function of providing an additionalmechanical support for the filtering mat.

The particular binders employed for the fibrous mat and the proportionsused are not critical. An alkyd resin has been found particularlysuitable for this purpose, but many other binders,

asaaoco both organic and inorganic, may be employed For example, othersynthetic and natural resinous materials may be used as well asmaterials such as starch, latex, asphalt, waxes, and the like, thevarious materials serving, in addition to their usual binding function,to lend various characteristics tothe mat. Mixtures of the variousbinders may be employed. The binders may be added to the furnish in anysuitable form such as libres, crystals,4 liquids, suspensions,emulsions, etc. Where the filter is to be employed under hightemperature conditions, an inorganic binder such as bentonite is ofparticular advantage. The binder may be one which is self-setting, suchas the alkyd resin referred to, or it may require further settingtreatments. Thus, for example, if one of the heat setting binders isemployed, the drying step may be carried out at a temperature sumcientlyhigh to cause setting of the binder. If a binder such as bentonite isused, the filter is subjected to firing temperatures, say, of 1200 F.

The proportion of the binder may vary widely depending upon the purposefor which the filter is to be used. In any event the binder should notbe present in suilicient amount to increase the flow resistance of thefilter to an undesirable extent. In the example given above, the binderin the stated proportion causes little increase in the flow resistanceof the filter, but adequately binds the fibers in the felted mat.

The size and character of the fibers may also vary depending upon theparticular qualities desired. Where the filter is to be employed toremove fine particles, fine mineral wool fibers are used. Thus, fibersof a diameter averaging between 4 and 6 microns have beeen found toprovide a filter which will remove from 99.5% to 99.7% of substantiallyuniform size particles of about 0.03 micron radius at a concentration ofapproximately milligrams per cubic meter of air. 'I'he air flow was atthe rate of 32 meters per minute and the unit had a filter area of about27 square inches.

Mineral wool fibers are preferred for the fibrous filtering layer butthey may, if desired, be intermixed with other fibers such as differentgrades of asbestos ber, sulphite pulp, cotton pulp,jute and manila pulpsand the like.

Where the air or other gas passing through the filter carries bothcoarse and fine particles, the filtering layer or mat may compriselayers of fibers of diierent size or character. As shown in Fig. 5, forexample, a layer 33 of fibers adjacent the matrix or foramlnous wall maybe of relatively fine fibers, providing minute interstices for theentrapment and removal of fine mirticles, and an outer layer 35overlying and substantially interfelted with the inner layer may be ofrelatively coarse fibers to entrap and remove relatively largerparticles and thus prolong the life and increase the efiiciency of thefilter unit. The second layer is preferably deposited similarly as thefirst, the furnish being changed or the matrix removed to a second vatto apply the second layer. It will be understood that as many differentinterfelted layers of fibers of different character may be employed asdesired.

Referring now to Fig. 3, a modification of the form of the filteringunit is shown. In this instance the supporting member comprises acorrugated screen or perforated element 36 onto which the lter mat 38 isdeposited. The method of forming the mat is similar to that previouslydescribed, except that the foraminous sheet or assaoee matrix 3l istemporarily sealed at its edges to a hood which is immersed in thefurnish and to which the suction is applied. The corrugations serve tostrengthen the filter unit and prevent its collapse. However, where thefilter is to be subjected to relatively low pressures or where othersupporting means are provided, the supporting sheet or matrix 36 may befiat or of other regular surface contour.

In Fig. 4 a further form of the lter unit is disclosed. In thisconstruction the element, similarly as in Fig. l, comprises a hollowbody having foraminous walls formed of screen or perforated sheetmaterial. Ihe body is shaped to define a plurality of wings I0, thefiltering mat being deposited over the entire area oi' the wings wherebythe filtering area is greatly increased without corresponding increaseof the diameter of the filtering unit. As will be understood, variousother shapes may similarly be employed to increase the filtering area orto pro vide other special functions. Due to the manner in which thefiltering mat is deposited fromthe wet furnish directly upon the matrix,adequate and uniform coverage of the matrix is obtained irrespective ofits particular shape.

Having thus described my invention in rather full detail, it will beunderstood that these details need not be strictly adhered to. but thatvarious changes and modifications will suggest themselves to one skilledin the art, all falling within the scope of the invention as dened bythe subloined claims.

What I claim is:

l. A filter for the removal of suspended particles from gases, saidfilter comprising a foraminous supporting member, a continuous mat ofrelatively mie minerai wool nbers with an uiterspersed binder in limitedamount overlying said member and conforming to the surface contoursthereof, and a substantially continuous mat of coarse mineral woolfibers overlying said first mat, the mats being interfelted at theirzones of contact.

2. A method of making a filter unit comprising collecting a mat ofmineral wool fibers and interspersed binder from an aqueous suspensionthereof onto a foraminous surface or a hollow filter element by drawingair and water from the interior of said element while said element isimmerd in said suspension. removing said element from said suspensionand drying said mat on said element, said binder being present in sminor amount in said suspension to bind the fibers of' the mat withoutexcessively increasing its flow resistance.

3. A method of making a filter unit comprising immersing a hollow filterelement including a foraminous surface area in a suspension oi iinemineral wool fibers and a binder, withdrawing air and liquid from theinterior of said element to cause collection of the fibers on theioraminous surface area thereof, immer-sing said element in a suspensionof coarser mineral wool fibers and a binder, again withdrawing air andliquid from the interior of said element to cause collection of a mat ofsaid coarser fibers on the mat of fibers first deposited, and drying themats on said element.

4. A filter for the removal of particulate matter, said filtercomprising a i'oraminous supporting member and a continuous,substantially uniform mat of wet felted mineral wool fibers and aninterspersed binder in minor amount sufficient to bind the fibers of themat without excessiveiy increasing its low resistance overlying saidmember in closely adherent relationship thereto.

5. A filter for the removal of suspended particles from gases, saidfilter comprising a foreminous supporting member of uneven surface comtour, and an interfelted mat of relatively fine mineral wool fibers andinterspersed binder in minor amount sufficient to bind the fibers of themat without excessively increasing its flow resistance overlying andconforming to the surface of the member.

PAUL F. MCDERMOTT.

` csnrrrrcira or CORRECTION.

lN-co u @met 21. 19u

PAUL F. ricnasno'rf.

*Itis hereby certified that error appears in the ofthe' Vabove numberedpatent requiring correction as follows: Page l, l line 14.5, for."interpersed read interspersed;

line 57, for "beson" read been-g read --flow-f; and that be'read withthis correction therein that the same releer sonnen; "'claimll., for"low" #orgasmus annessi ore or ene ease 1n the Patent office.

lith day 'of' December, A. D. 194.5.

printed specification first page 2, second page 5, second column, line52, the said Int-tors Patent should may conform to the rec- LeslieFrazer First Assistant Commissioner of` Patents.

assaoee matrix 3l is temporarily sealed at its edges to a hood which isimmersed in the furnish and to which the suction is applied. Thecorrugations serve to strengthen the filter unit and prevent itscollapse. However, where the filter is to be subjected to relatively lowpressures or where other supporting means are provided, the supportingsheet or matrix 36 may be fiat or of other regular surface contour.

In Fig. 4 a further form of the lter unit is disclosed. In thisconstruction the element, similarly as in Fig. l, comprises a hollowbody having foraminous walls formed of screen or perforated sheetmaterial. Ihe body is shaped to define a plurality of wings I0, thefiltering mat being deposited over the entire area oi' the wings wherebythe filtering area is greatly increased without corresponding increaseof the diameter of the filtering unit. As will be understood, variousother shapes may similarly be employed to increase the filtering area orto pro vide other special functions. Due to the manner in which thefiltering mat is deposited fromthe wet furnish directly upon the matrix,adequate and uniform coverage of the matrix is obtained irrespective ofits particular shape.

Having thus described my invention in rather full detail, it will beunderstood that these details need not be strictly adhered to. but thatvarious changes and modifications will suggest themselves to one skilledin the art, all falling within the scope of the invention as dened bythe subloined claims.

What I claim is:

l. A filter for the removal of suspended particles from gases, saidfilter comprising a foraminous supporting member, a continuous mat ofrelatively mie minerai wool nbers with an uiterspersed binder in limitedamount overlying said member and conforming to the surface contoursthereof, and a substantially continuous mat of coarse mineral woolfibers overlying said first mat, the mats being interfelted at theirzones of contact.

2. A method of making a filter unit comprising collecting a mat ofmineral wool fibers and interspersed binder from an aqueous suspensionthereof onto a foraminous surface or a hollow filter element by drawingair and water from the interior of said element while said element isimmerd in said suspension. removing said element from said suspensionand drying said mat on said element, said binder being present in sminor amount in said suspension to bind the fibers of' the mat withoutexcessively increasing its flow resistance.

3. A method of making a filter unit comprising immersing a hollow filterelement including a foraminous surface area in a suspension oi iinemineral wool fibers and a binder, withdrawing air and liquid from theinterior of said element to cause collection of the fibers on theioraminous surface area thereof, immer-sing said element in a suspensionof coarser mineral wool fibers and a binder, again withdrawing air andliquid from the interior of said element to cause collection of a mat ofsaid coarser fibers on the mat of fibers first deposited, and drying themats on said element.

4. A filter for the removal of particulate matter, said filtercomprising a i'oraminous supporting member and a continuous,substantially uniform mat of wet felted mineral wool fibers and aninterspersed binder in minor amount sufficient to bind the fibers of themat without excessiveiy increasing its low resistance overlying saidmember in closely adherent relationship thereto.

5. A filter for the removal of suspended particles from gases, saidfilter comprising a foreminous supporting member of uneven surface comtour, and an interfelted mat of relatively fine mineral wool fibers andinterspersed binder in minor amount sufficient to bind the fibers of themat without excessively increasing its flow resistance overlying andconforming to the surface of the member.

PAUL F. MCDERMOTT.

` csnrrrrcira or CORRECTION.

lN-co u *Itis hereby certified that error appears in the ofthe' Vabovenumbered patent requiring correction as follows: Page l, l line 14.5,for ."interpersed read interspersed;

line 57, for "beson" read been-g read --flow-f; and that be'read withthis correction therein that the same releer sonnen; "'claimll., for"low" #orgasmus annessi ore or ene ease 1n the Patent office.

lith day 'of' December, A. D. 194.5.

@met 21. 19u

PAUL F. ricnasno'rf.

printed specification first page 2, second page 5, second column, line52, the said Int-tors Patent should may conform to the rec- LeslieFrazer First Assistant Commissioner of` Patents.

